Conventional friction welding relies on very high magnitude applied forces and mechanical torques, or, alternatively, lateral vibratory forces, to produce the desired hot forging temperature and pressure conditions within a weld zone. The relative motion of the contacting surfaces in the weld zone is typically slow, and, as a result, a large fraction of the heat generated is lost during the welding process, i.e., by thermal conduction into the base metal(s), consumable filler material and/or non-consumable probe. The corresponding broadening of the width, increase in the time, and increase in temperature of the weld heat-affected zone (HAZ) can be highly undesirable, particularly for materials that are susceptible to chemical dilution, thermal sensitization or helium embrittlement. Such thermal inefficiency also increases the power required to deposit a desired bead. In addition, the size and weight of the tooling required to apply the necessary normal forces and vibratory motion and/or torque will tend to be substantial.
Conventional resistance welding relies on a combination of large electrical currents and applied forces to produce the required temperature and pressure conditions for hot forging within a weld zone. Due to the lack of relative motion between the mating surfaces, resistance welding typically provides no significant cleaning action of the mating surfaces and does not tend to produce a well homogenized material in the weld zone. As a result, even higher applied forces and higher corresponding contact pressures are required to obtain an internally clean weld nugget having acceptable mechanical properties for demanding applications. Because of the high applied forces required by these conventional welding processes, the tooling to apply them is correspondingly large and heavy and generally inappropriate for remotely-applied welds in limited-access areas where a semi-solid state weld may be required.
With these conventional semi-solid state welding methods, any significant reduction in the size and weight of the associated tooling requires a corresponding reduction in the weld size and/or the process productivity. A simplistic “scaling” approach for developing tools for confined spaces will tend to result in tooling of a size which is impractical or impossible to use for remote field applications in limited access areas. For example, tooling of size and strength sufficient to provide satisfactory weld size and productivity will tend to be too large to operate in confined areas. Conversely, tooling that has been reduced in size to a degree sufficient to operate in confined areas will tend to exhibit weld size and productivity that are undesirable or unacceptable for meeting “critical path schedules.”
However, no apparatus or method heretofore has been known to overcome the problems of either conventional resistance or friction semi-solid state welding with respect to production of weld joints or application of weld cladding in remote and/or confined locations where process tooling and delivery equipment size, weight, and reaction force values must be kept to a minimum, while also providing high productivity and high weld quality.